Astute service providers realize that

Astute service providers realize that the continued support of legacy X.25 and asynchronous network element using separate operations network is cost(16).For example,the maintenance of multiple networks can require additional staff. Often, this staff must be trained on multiple vendor technologies, sometimes requiring parallel groups specializing in each (17) .Hence, additional maintenance procedures must be maintained and administrative records are (18) .The duplication of transport facilities to carry (19)network traffic is an inefficient use of resources. And not surprisingly, more technologies installed in a central office means the necessity for more physical space, and an increase in power connections and power consumption migration of these (20) network elements to IP-based DCns is alogical strategy.空白处（17）应选择（）

AA.line
Bplatform
Csever
Dswitch

参考答案

参考解析：

分析敏锐的供应商认识到，昂贵的成本不允许他们继续使用分隔的业务网络支持老版本的X.25协议和异步网络元素。例如，维护多个网络需要更多的人员。通常情况下，这些人员必须接受多家提供商的培训，有时甚至需要在每个平台上安排多个并行的工作团队。因此，必须维持额外的维护过程，且复制多个管理记录。成倍的传输设备用在交叉的网络通信中，这是资源的无效使用。而且，毫不奇怪的是，更多的技术安装在一个中心办公室，这意味着需要更大的物理空间，增大的电力连接和消耗。因此，把这些老的网络设备移植到基于IP的数据通信网络中是不符合逻辑的策略。

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